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End date: 2022 × Start date: 2020 × DDC: 500 × DDC: 620 × Type: Text ×

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    Numerical simulation of TEM images for In(Ga)As/GaAs quantum dots with various shapes
    (Dordrecht [u.a.] : Springer Science + Business Media B.V, 2020) Maltsi, Anieza; Niermann, Tore; Streckenbach, Timo; Tabelow, Karsten; Koprucki, Thomas
    We present a mathematical model and a tool chain for the numerical simulation of TEM images of semiconductor quantum dots (QDs). This includes elasticity theory to obtain the strain profile coupled with the Darwin–Howie–Whelan equations, describing the propagation of the electron wave through the sample. We perform a simulation study on indium gallium arsenide QDs with different shapes and compare the resulting TEM images to experimental ones. This tool chain can be applied to generate a database of simulated TEM images, which is a key element of a novel concept for model-based geometry reconstruction of semiconductor QDs, involving machine learning techniques.
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    Detecting striations via the lateral photovoltage scanning method without screening effect
    (Dordrecht [u.a.] : Springer Science + Business Media B.V, 2021) Kayser, S.; Farrell, P.; Rotundo, N.
    The lateral photovoltage scanning method (LPS) detects doping inhomogeneities in semiconductors such as Si, Ge and SixGe1−x in a cheap, fast and nondestructive manner. LPS relies on the bulk photovoltaic effect and thus can detect any physical quantity affecting the band profiles of the sample. LPS finite volume simulation using commercial software suffer from long simulation times and convergence instabilities. We present here an open-source finite volume simulation for a 2D Si sample using the ddfermi simulator. For low injection conditions we show that the LPS voltage is proportional to the doping gradient. For higher injection conditions, we directly show how the LPS voltage and the doping gradient differ and link the physical effect of lower local resolution to the screening effect. Previously, the loss of local resolution was assumed to be only connected to the enlargement of the excess charge carrier distribution.
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    Correction to: Numerical simulation of TEM images for In(Ga)As/GaAs quantum dots with various shapes
    (Dordrecht [u.a.] : Springer Science + Business Media B.V, 2021) Maltsi, Anieza; Niermann, Tore; Streckenbach, Timo; Tabelow, Karsten; Koprucki, Thomas
    Correction to: Optical and Quantum Electronics (2020) 52:257 https://doi.org/10.1007/s11082-020-02356-y
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    One-shot phase-recovery using a cellphone RGB camera on a Jamin-Lebedeff microscope
    (San Francisco, California, US : PLOS, 2019) Diederich, Benedict; Marsikova, Barbora; Amos, Brad; Heintzmann, Rainer
    Jamin-Lebedeff (JL) polarization interference microscopy is a classical method for determining the change in the optical path of transparent tissues. Whilst a differential interference contrast (DIC) microscopy interferes an image with itself shifted by half a point spread function, the shear between the object and reference image in a JL-microscope is about half the field of view. The optical path difference (OPD) between the sample and reference region (assumed to be empty) is encoded into a color by white-light interference. From a color-table, the Michel-Levy chart, the OPD can be deduced. In cytology JL-imaging can be used as a way to determine the OPD which closely corresponds to the dry mass per area of cells in a single image. Like in other interference microscopy methods (e.g. holography), we present a phase retrieval method relying on single-shot measurements only, thus allowing real-time quantitative phase measurements. This is achieved by adding several customized 3D-printed parts (e.g. rotational polarization-filter holders) and a modern cellphone with an RGB-camera to the Jamin-Lebedeff setup, thus bringing an old microscope back to life. The algorithm is calibrated using a reference image of a known phase object (e.g. optical fiber). A gradient-descent based inverse problem generates an inverse look-up-table (LUT) which is used to convert the measured RGB signal of a phase-sample into an OPD. To account for possible ambiguities in the phase-map or phase-unwrapping artifacts we introduce a total-variation based regularization. We present results from fixed and living biological samples as well as reference samples for comparison.